1. Field of the Invention
The present invention relates to an optical information processing method of recording and/or reproducing information by irradiating a light beam to an optical record medium, and an apparatus therefor.
2. Related Background Art
FIG. 1 shows a schematic diagram of a prior art optical information processor. In FIG. 1, numeral 21 denotes a laser light source such as a semiconductor laser, numeral 22 denotes a collimator lens for collimating a light beam emitted from the laser light source 21, numeral 23 denotes a half-mirror, numeral 24 denotes an objective lens, numeral 25 denotes a lens actuator for driving the objective lens 24 along an optical axis of the lens and perpendicularly thereto, numeral 26 denotes a disk shaped optical record medium (disk), numeral 27 denotes a motor for rotating the disk 26, numeral 28 denotes a focusing lens for focusing a light reflected by the disk 26, numeral 29 denotes a photo-detector, numeral 34 denotes a control circuit for feeding the output of the photo-detector 29 back to the lens actuator 25, numeral 35 denotes a controller, and numeral 37 denotes a laser driver.
In the apparatus of FIG. 1, when information is to be recorded, the controller 35 causes the laser light source 21 to emit the light beam modulated with record information in accordance with a command from an external device. The emitted light beam passes through the collimator lens 22 and the half-mirror 23 and focused onto the disk 26 as a fine spot by the objective lens 24. Record bits corresponding to the record information are formed on the disk 26 in an optically detectable form by the irradiation of the light beam. The light beam reflected by the disk 26 passes through the objective lens 24, reflected by the half-mirror 23 and focused onto the photo-detector 29 by the focusing lens 28. The photo-detector 29 detects a focusing servo signal and a tracking servo signal. Those detected signals are fed back to the lens actuator 25 through the control circuit 34 so that the auto-focusing is done to allow the light spot to be exactly focused onto the disk 26 and the auto-tracking is done to allow the light spot to exactly trace a preformed track on the disk 26.
When information is to be reproduced, the controller 35 causes the laser light source 21 to emit a light at a constant intensity which is low enough to assure that no information is recorded, through the laser driver 37. The information recorded on the disk 26 is reproduced by the photo-detector 29 while the auto-focusing and the auto-tracking are done as are in the record mode. When information is not to be recorded nor reproduced, the laser light source emits a light at a low intensity as it does in the reproduce mode and the apparatus stands by until a record or reproduce command is issued while it makes auto-focusing and auto-tracking controls.
The focusing and tracking servo signals may be detected in the following manner. FIG. 2 shows a block diagram of the control circuit 34 of FIG. 1. In FIG. 1, the focusing lens 28 comprises a rotary symmetric lens and a cylindrical lens having a base line thereof arranged to make an angle of 45.degree. with respect to the track of the disk 26. Accordingly, the reflected light focused by the focusing lens 28 creates an astigmatism, and the photo-detector 29 is arranged at a position of a minimum scatter circle of the reflected light when the spot is exactly focused on the disk 26. A photosensing plane of the photo-detector 29 is divided into four sensors 29a, 29b, 29c and 29d. The spot of the reflected light forms a circle shown by a solid line in an in-focus state, and in a defocus state it forms an ellipse shown by a broken line having a major axis orthogonal to the direction of defocusing. The outputs of the diagonal sensors 29a and 29c, and 29b and 29d are added together by summing amplifiers 30 and 31, respectively, and the sum signals are differentiated by a differential amplifier 32 so that the focusing servo signal is produced. The focusing servo signal is supplied to a focusing coil 42 of the actuator 25 through a focusing driver 33 and the objective lens 24 is moved along the optical axis in accordance with the focusing servo signal so that the auto-focusing control is made.
A divide line D of the photo-detector 29 corresponds to the direction of the track of the disk 26. As the light spot on the disk 26 deviates from the track, light distributions on the left and right sides of the divide line D are unbalanced depending on the direction of deviation. Thus, by adding the outputs of the sensors 29a and 29d, and 29b and 29c by adders 38 and 39 and differentiating the sum signals by a differential amplifier 40, the tracking servo signal is produced The tracking servo signal is supplied to a tracking coil 43 of the actuator 25 through a tracking driver 41, and the objective lens 24 is driven in a direction orthogonal to the optical axis and cross the track in accordance with the tracking servo signal so that the auto-tracking control is made.
Such an optical information processor is shown in detail in U.S. Pat. No. 4,293,944. In U.S. Pat. No. 4,205,338 and U.S. Pat. No. 4,527,263, one disk circumference of detected tracking servo signals are stored and the auto-tracking means is driven in accordance with the stored servo signals to record or reproduce information.
However, in such a prior art apparatus, since the light beam is irradiated to the medium even in a stand-by state in which information is not recorded or reproduced, durability of the light source is short. In order to avoid the above problem, the irradiation of the light beam to the medium may be stopped during the stand-by time, but since the focusing and tracking servo signals are not detected during that period, the objective lens is at a position which is totally independent from the movement of the medium. As a result, when the light beam is again irradiated to the medium to resume recording or reproducing, a time is required before the auto-focusing and auto-tracking servos are pulled in.